JPH0529588B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a four-wheel steering system for a vehicle, and more particularly to a four-wheel steering system for a vehicle equipped with a mechanism that can vary the steering ratio of front and rear wheels. This invention relates to a four-wheel steering device.

(Prior Art) Conventionally, this type of four-wheel steering device includes a steering device that steers the front wheels and a steering device that steers the rear wheels, as disclosed in, for example, Japanese Patent Application Laid-Open No. 55-91457. It is known that the vehicle is connected to a rear wheel steering device via a link mechanism having a lever member, and the steering ratio of the front and rear wheels is changed by changing the lever ratio of the lever member according to the vehicle speed.

However, in the conventional system described above, since a lever member is used as a means for changing the steering ratio according to the vehicle speed, the control mechanism is complicated, and in order to change the lever ratio of the lever member,
Since a sliding mechanism is used, backlash is likely to occur, which is undesirable in terms of control reliability.

(Objective of the Invention) Therefore, an object of the present invention is to provide a four-wheel steering device for a vehicle that has a simple structure and a highly reliable steering ratio changing mechanism.

(Structure of the Invention) A four-wheel steering device for a vehicle according to the present invention includes a front wheel steering system,
a rear wheel steering system; and a control differential device that controls the operation of the rear wheel steering system in accordance with the operation of the front wheel steering system, and the control differential device includes a first rotor as a control rotating section.
and a second gear and a differential casing gear, one of the three gears is connected to the front wheel steering system, and the other gear is connected to the rear wheel steering system. and the remaining 1
The two gears are connected to the front wheel steering system via a bendable joint mechanism, and the vehicle is characterized by comprising means for bending the joint mechanism in accordance with parameters related to the running state of the vehicle.

(Effects of the Invention) The four-wheel steering system for a vehicle of the present invention having the structure explained above includes a differential device as a part of the steering ratio changing mechanism, and one gear in the differential device is configured to rotate as described above. Since the operation is controlled by a bendable joint mechanism, the rear wheels can be steered with high reliability and the steering ratio can be changed with a simple structure. Note that if an actuator is provided in the joint mechanism and the actuator is controlled by a controller according to the vehicle speed to control the turning angle of the joint mechanism, the steering ratio can be easily changed according to the vehicle speed. be able to.

(Embodiment) Hereinafter, a four-wheel steering system for a vehicle according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is an overall schematic diagram of a four-wheel steering system for a vehicle according to an embodiment of the present invention. In FIG. 1, reference numeral 1 indicates a front wheel steering system for steering left and right front wheels 2L, 2R. This front wheel steering system 1 includes a steering wheel 3 that is steered by the driver.
, a pinion and rack mechanism 4 that converts the steering force of the steering wheel 3 into reciprocating motion in the vehicle width direction, that is, in the left-right direction, and transmits the same; Tie rods 5L, 5R, and one end of each tie rod 5L,
At the tip of 5R, there are knuckle arms 6L, 6R whose other ends are connected to the left and right front wheels 2L, 2R, respectively, so that the left and right front wheels 2L, 2R are steered left and right in accordance with the steering of the steering wheel 3. It's summery.

On the other hand, reference numeral 7 indicates a rear wheel steering system that steers the left and right rear wheels 8L, 8R.
A connecting member 1 operatively connected to the rack 4a of the front wheel steering system 1 by an interlocking mechanism 9 for causing the steering of the front wheels L and 8R to follow the steering of the front wheels 2L and 2R.
0. At each end of this connecting member 10,
The left and right tie rods 12L, 12R are connected at their base ends. This tie rod 12L, 1
At the tip of 2R, there are knuckle arms 13L and 13R.
are connected at one end, and these knuckle arms 13L, 13R support rear wheels 8L, 8R at the other end. With the above configuration,
The left and right rear wheels 8L and 8R are steered left and right in accordance with the steering of the steering wheel 3.

The interlocking mechanism 9 is a rack 4a of the front wheel steering system 1.
An input shaft 20 is operatively connected to the rear wheel steering system 1, and an output shaft 21 is operatively connected to the coupling member 10 of the rear wheel steering system 1. A differential gearing 22 is provided between the input and output shafts 20 and 21. The differential gear device 22 includes an input bevel gear 23 coupled to the input shaft 20, an output bevel gear 24 coupled to the output shaft 21, and a bendable joint-type control mechanism 25 of the Fucks shaft joint type. A differential casing gear 26 is operatively connected to the input shaft 20 via a differential casing gear 26.

The joint type control mechanism 25 is arranged parallel to the input shaft 20, and includes an input shaft 31 connected to the shaft 20 by a gear 30, and an input shaft 31 arranged coaxially with the input shaft 31 and connected to the differential shaft 20. An output shaft 33 is connected to the casing gear 26 by a gear 32. As shown in FIG. 2, the input shaft 31 has a first link 34, the output shaft 33 has a second link 35, and these first and second links 34 and 35 each have a universal joint 36. , 39, 38. The second link 35 is provided with an angle adjustment mechanism 40, and the angle α of the second link 35 with respect to the line connecting the shafts 31 and 33 is adjusted by the angle adjustment mechanism 40. . In order to allow the second link 35 to swing around the joint 39 when adjusting the angle α in this manner, the first link 34 is constructed in a telescoping manner as shown in FIG. It is flexible.

The angle adjustment mechanism 40 has one end connected to the second link 3.
The actuating rod 41 has an actuating rod 41 connected to the actuating rod 5, and a rack 42 is connected to the other end of the actuating rod 41. The rack 42 is actuated by a motor 45 via a pinion 43 and a gear 44 connected to the pinion 43 to swing the second link 35 via the actuation rod 41. A controller 46 is connected to the motor 45, and a vehicle speed sensor 47 that detects the vehicle speed and outputs a vehicle speed signal _Sv is connected to the controller 46. The controller 46 is
The power supply 48 receives the vehicle speed signal S _v and supplies a current C with a magnitude corresponding to the vehicle speed indicated by the vehicle speed signal S _v .
is supplied to the motor 45 from above. The motor 45 is
The second
Adjust the angle α of the link 35.

When configured as above, the input shaft 20
rotation angle (θ _A ), rotation angle of the differential casing gear 26 (θ _B ), rotation angle of the output shaft (θ _C ), rotation angle of the input shaft 31 (θ _A ′), rotation of the output shaft 33 angle (θ _B ′), rotation angle of the first link 34 (θ ₁ ),
The rotation angle (θ ₂ ) of the second link 35 and the steering angle (θ _R ) of the rear wheels are determined by the following equations.

The rotation angles of the input shaft 31 and output shaft 33 of the joint type control mechanism 25 are as follows.

〓θ _A ′＝〓α ₁・〓θ ₁ 〓θ ₁ =〓α ₂・〓θ ₂ 〓θ ₂ =〓α・〓θ _B ′ ∴θ _B ′＝〓 ^-1 (1/〓α ₁・〓 α ₂・〓α・〓θ _A ′)=
〓 ^-1 (C・〓θ _A ′)... However, C=1/〓α ₁・〓α ₂・〓α The overall system is as follows.

θ _A = γ ₁ θ _A ′ θ _B = γ ₂ θ _B ′ 2θ _B = θ _A + θ Substituting _{the C} formula into the above formula and organizing it, θ _C = 2γ ₂・〓 ^-1 (C・〓θ _A ′ )−γ ₁・θ _A ′ Then, assuming θ _R = θ _C /35, θ _R = 1/35 {2γ ₂・〓 ^-1 (C・〓θ _A ′)−γ ₁ θ _A ′
} becomes.

However, γ ₁ is the reduction ratio of the gear 30 γ ₂ is the reduction ratio of the gear 32 In this way, the steering angle θ _R of the rear wheels 8L and 8R is expressed by a trigonometric function of the steering angle θ _H of the steering wheel 3, For example, if the angle α is 15°, 10°, 5°, and 0°, the relationship between the steering angle θR and the steering angle _θH is as shown in FIG. Therefore, if the angle α is made smaller as the vehicle speed is lower, and increased as the vehicle speed is faster, a desired steering angle θ _R of the rear wheels can be obtained depending on the vehicle speed.
In addition, in FIG. 3, the negative sign of the steering angle θ _R indicates an opposite phase to the steering of the front wheels.

The rear wheel steering system 7 is provided with a rear wheel power assist mechanism 50, and this power assist mechanism 50 has a power cylinder device 51. This power cylinder device 51 includes a cylinder case 52 fixed to the vehicle body and extending in the vehicle width direction;
A piston 5 is provided integrally with the connecting member 10 and is slidably fitted into the cylinder case 52.
3, and a left chamber 52L and a right chamber 52R partitioned by the piston 53. A hydraulic line 54 is provided in the left chamber 52L and right chamber 52R.
L and 54R are connected to each other.

In the figure, reference numeral 60 indicates an oil reservoir, and from this oil reservoir 60, an oil supply line 62 and a drain line 63, each provided with a pump 61, extend. This oil supply line 62 and drain line 63 and the above hydraulic lines 54L, 54R
A switching valve 64 is provided between them, and this switching valve 64 functions to connect one of the hydraulic lines 54L and 54R to the oil supply line 62 and the other to the drain line 63. The switching valve 64 is connected to the output shaft 21,
It is desirable that the connection of the above line be switched as the shaft 21 rotates forward or reverse.

[Brief explanation of drawings]

FIG. 1 is an overall schematic diagram of a four-wheel steering device according to an embodiment of the present invention, and FIG. 2 is a four-wheel steering device shown in FIG.
FIG. 3, an enlarged view showing details of the joint type control mechanism used in the wheel steering device, is a graph showing the front and rear wheel steering ratio characteristics obtained by the above embodiment. DESCRIPTION OF SYMBOLS 1... Front wheel steering system, 7... Rear wheel steering system, 22... Differential device, 23, 24... Bevel gear, 25... Joint type control device, 26... Differential casing gear.

Claims (1)

[Scope of Claims] 1. A front wheel steering system, a rear wheel steering system, and a control differential device that controls the operation of the rear wheel steering system according to the action of the wheel steering system, the control differential device controlling the operation of the rear wheel steering system according to the action of the wheel steering system. It has three gears as a rotating part: first and second gears and a differential casing gear, one of these three gears is connected to the front wheel steering system, and the other gear is connected to the rear wheel steering system. The remaining one gear is connected to the front wheel steering system via a bendable joint mechanism, and includes means for bending the joint mechanism in accordance with parameters related to the running state of the vehicle. Four-wheel steering system for vehicles. 2. The four-wheel steering system for a vehicle according to claim 1, wherein the parameter related to the running state of the vehicle is a vehicle speed.